Trehalose
In plain terms
A sugar that some plants and animals make to survive drying out, used as a gentle humectant that holds water and helps protect the skin barrier. It is food-grade and very well tolerated.
What the evidence shows
Trehalose is a sugar built from two glucose units that desert plants, tardigrades, and other organisms produce to survive extreme drying, essentially standing in for water and protecting proteins and membranes until moisture returns. In skincare it works as a humectant, drawing and holding water, and there is some evidence it also helps steady the skin barrier under stress. Its safety is exceptionally well established because it is a food. Regulators treat trehalose as generally recognized as safe as a food ingredient, animal studies found no toxicity by mouth or by injection, and it is trusted enough to be used as a stabilizer in injectable and eye medicines. On skin its irritation record is clean across skin types. There is no hormone, cancer, or contamination concern, and the only effect ever noted from large oral doses is mild digestive upset, which has nothing to do with a small amount in a moisturizer. It is a gentle, food-grade hydrator.
On the label
Listed as trehalose, usually among the humectants in a hydrating serum or moisturizer. It is a food-grade sugar with an exceptionally clean tolerance record, so it is a safe pick even for sensitive skin.